The present invention relates to a process and associated apparatus for forming lamp capsules, such as in the manufacture of miniature arc lamps, and to lamp capsules made by such a process. More particularly the present invention relates to such a process and associated apparatus using a combination molding and press sealing technique.
A lamp capsule with a lead assembly is typically formed with the use of a hollow glass blank. In the case of miniature arc lamps the glass blank typically is formed of fused quartz. One prior art technique for forming the lamp capsule is by shaping the glass blank by rolling it in contact with a contoured copper mold. Thereafter, the upper hemisphere of the capsule is press sealed. The "rolling" technique has several disadvantages one of the key of which is that the technique is very labor intensive. The technique is thus not readily adapted to automated operation. In using the "rolling" technique the capsule is shaped and is thereafter cooled requiring subsequent reheating and reshaping to complete the capsule. This prior art technique is quite apt to provide inconsistencies in the proper size, shape and form of the capsule from capsule to capsule. For example, the capsule wall thickness might vary. This then meant that the alignment of the capsule was not maintained accurately during the subsequent pressing operation. Also, if the process heat was not uniform, significant variations in capsule geometry and volume were inevitable.